A hybrid vehicle may be started via an electric machine that both propels the vehicle and acts as a starter. The electric machine may be directly coupled to the engine it starts or it may rotate the engine via a gear set or a clutch. The electric machine may start the engine after the vehicle is initially activated or it may start the engine after the vehicle has been activated for some period of time. However, there may be conditions when the electric machine does not have the capability of starting the engine. For example, the electric machine may not have capability to start the engine if the electric machine is degraded or if the electric machine has insufficient torque to rotate the engine. Therefore, it may be desirable to provide a way of increasing the probability of being able to start the engine.
The inventors herein have recognized the above-mentioned disadvantages of starting an engine of a hybrid vehicle with a sole electric machine and have developed an engine starting method, comprising: starting an engine with a first starting device in response to a high voltage system being capable of starting the engine, the first starting device having a higher torque capacity than a second starting device; and starting the engine with the second starting device in response to a DC/DC converter outputting a desired voltage.
By providing two electric machines and a DC/DC converter that can transfer power from a high voltage power system to a low voltage power system, it may be possible to provide the technical result of improving the possibility of engine starting. In one example, the output of the DC/DC converter may be a basis for determining that one of the two electric machines is ready to crank the engine. Alternatively, capability of a high voltage power system is assessed to determine which starting device should be used to start the engine. Thus, the engine may be cranked via the first or second electric machine depending on vehicle operating conditions. For example, an electric machine with a lower torque capacity may crank the engine if a high torque capacity electric machine is in a degraded condition.
The present description may provide several advantages. For example, the approach may provide a way of arbitrating which of two electrical machines is best suited to start an engine in response to present vehicle operating conditions. Additionally, the approach may include different arbitration schemes depending on if the engine is to be immediately started or started sometime after the vehicle has been activated. The approach may also provide improve vehicle durability by limiting use of an electric machine during selected conditions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.